The proposed studies examine structure-function relationships and the expression of lipoprotein lipase (LPL). The goal of the first aim is to determine a high resolution structure of the enzyme. Towards this goal, isolated domains are being readied for NMR spectroscopy and novel lipase molecules prepared for crystallization trials. Other studies will also be performed using unique lipase constructs that form the basis of a general approach to design and construct active lipases that address specific issues of lipase structure- a general approach to design and construct active lipases that address specific issues of lipase structure function relationships. Lessons learned from such biochemical studies are extended in Aim 2, to ask how LPL function inc ells and whole animals is a consequence of enzyme structure. Specific questions regarding the role function inc ells and whole animals is a consequence of enzyme structure. Specific questions regarding the role of LPL in normal and pathophysiology are addressed. Finally, in the last aim, a molecular genetic approach is used to identify trans-acting factors affecting the expression of mouse LPL activity. The ultimate goal of this aim is to determine whether such loci contribute to genetic variations in triglyceride levels in human families, and if they can explain the occurrence of LPL deficiency in familial combined hyperlipidemia. Specific objectives are to: i) determine the 3-dimensional structure of LPL, delineate domain interactions during lipolysis, and localize heparin and co-factor binding sites; ii) determine the biochemical basis for lipase physiological functions, such as tissue localization, lipoprotein specificity, and contribution to monocyte adhesion; and iii) identify genetic loci affecting expression. These goals are directly related to an overall theme of the regulation of triglyceride metabolism, since LPL plays a crucial role in lipoprotein metabolism. Knowledge of LPL structure-function relationships and the identification of modulators of lipase activity will enhance our understanding of triglyceride metabolism as a whole.